Four persons were arrested on Wednesday by the anti-terror police in connection with the July 7 bombings in London in which 52 people were killed.
Two men and a woman were arrested in West Yorkshire while another man was arrested in the West Midlands.
They were held on suspicion of commission, preparation, or instigation of acts of terrorism under the Terrorism Act, 2000.
All four suspects were taken to a central London police station where they will be interviewed by anti-terror officers.
The arrests of the two men - aged 30 and 34 - and the 29-year-old woman in West Yorkshire took place at 7 a.M (1230 IST). Five houses in the area were searched, including two in Dewsbury, two in Beeston - south Leeds, and one in Batley.
Two flats in Birmingham were also searched, the Metropolitan Police said. The fourth man arrested is 22 years old.
No armed officers were used in today's operation.
"This was a pre-planned, intelligence-led operation involving the Metropolitan Police Service's Counter Terrorism Command and the counter terrorism units in West Yorkshire and the West Midlands," a police spokesman said.
"We are continuing a painstaking investigation with a substantial amount of information being analysed and investigated.
"As we have said previously, we are determined to follow the evidence wherever it takes us to identify any other person who may have been involved, in any way, in the terrorist attacks," the spokesman said.